AbstractCoagulation abnormalities after successful resuscitation from cardiac arrest may be associated with unfavorable neurologic outcome. We investigated a potential association of activated partial thromboplastin time (aPTT) with neurologic outcome in adult cardiac arrest survivors. Therefore, we included all adults ≥18 years of age who suffered a nontraumatic cardiac arrest and had achieved return of spontaneous circulation between January 2013 and December 2018. Patients receiving anticoagulants or thrombolytic therapy and those subjected to extracorporeal membrane oxygenation support were excluded. Routine blood sampling was performed on admission as soon as a vascular access was available. The primary outcome was 30-day neurologic function, assessed by the Cerebral Performance Category scale (3–5 = unfavorable neurologic function). Multivariable regression was used to assess associations between normal (≤41 seconds) and prolonged (>41 seconds) aPTT on admission (exposure) and the primary outcome. Results are given as odds ratio (OR) with 95% confidence intervals (95% CIs). Out of 1,591 cardiac arrest patients treated between 2013 and 2018, 360 patients (32% female; median age: 60 years [interquartile range: 48–70]) were eligible for analysis. A total of 263 patients (73%) had unfavorable neurologic function at day 30. aPTT prolongation >41 seconds was associated with a 190% increase in crude OR of unfavorable neurologic function (crude OR: 2.89; 95% CI: 1.78–4.68, p < 0.001) and with more than double the odds after adjustment for traditional risk factors (adjusted OR: 2.01; 95% CI: 1.13–3.60, p = 0.018). In conclusion, aPTT prolongation on admission is associated with unfavorable neurologic outcome after successful resuscitation from cardiac arrest.